Optical brightening agents (OBA's) or fluorescent whitening agent (FWA's) have chemical properties that absorb light in the ultraviolet region (340-370 nm) and then re-emitting it back into the visible spectrum, usually in the color blue or indigo (420-470 nm). The absorption and re-emission happen at a rapid pace unlike the slow phosphorescence behaviour. The newly added blue light compensates the yellowness of paper products and produces a net whitening effect that is observable to the naked eye.